Warm air rises and draws cooling air in. Most things that use air for insulation works by trapping the air.
If you just place the pails together the walls will be in contact and there'll be no airspace.

When I nest my two buckets, there's about a 3/8" gap between the walls. How about some of that expandable spray foam? Drill a couple strategic 1/8" holes though the outside bucket and insert the nozzle. I agree that trapping air is the key.

When I was doing mini mashes, I was using my bottling bucket like we discussed. I wrapped with a sleeping bag, but still lost 10-15 degrees over an hour. Not a huge deal for minimashes, because I was adding extract anyway. But for AG, you don't want it to drop. Two buckets would lose too much heat, but if you throw a blanket around it, it would help.

__________________Broken Leg BreweryGiving beer a leg to stand on since 2006

This is an interesting discussion on how to make a MLT other than the usual cooler-conversion route. And not to throw a spanner in that, but...

Wal-Mart sells five-gallon Rubbermaid coolers for ridiculously cheap. The orange and blue ones, I think are $16, but the "hunter's green" ones get cheaper every time I go back: $9.79 on last visit. I bought one for an HLT, but before they got *that* cheap.

At that price, I keep thinking I should get another, but I don't think I'd have any use for it.

I agree 5 gal coolers are cheap. I bought mine today for just under $20 (I'm too impatient to wait for sales). It sounds like a rubber stopper, SS braid and short piece of copper will be less than $15. But it you want even cheaper you can buy a large nylon grain bag for a few dollars and just use the spigot as included with the cooler. Thats what I'm going to do for now for my PM brews.
Craig

I used my 5 gallon Rubbermaid round again today for an AG Bitters. Once again, it performed perfectly...holding my mash temp at 156 for 45 minutes before finally giving up 1 degree (down to 155)for the next twenty minutes.